Tone frequency control system for electronic musical instruments



Nov. 29, 1966 T. J. GEORGE 3,288,904

TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS FiledSept. 25, 1962 4 Sheets-Sheet 1 Ali. MIC.

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TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS FiledSept. 25, 1962 4 Sheets-Sheet 2 Q (Q ("I P V :s 92 O Q) SWKTCH 41INVENTOR. 9 THOMAS J. GEORGE 9' BY Nov. 29, 1966 -r. J. GEORGE 3,288,904

TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS FiledSept. 25, 1962 4 Sheets-Sheet 5 u) E m P M A P m E {if g .3 (\1 1 i W Zw v LL. U

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INVENTOR. THOMAS J. GEOEG E AMM (N Nov. 29, 1966 T. J. GEORGE 3,283,904

TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICAL INSTRUMENTS MALE.VOICE FEMALE VOICE INVENTOR. THOMAS J. GEORGE United States Patent3,288,904 TONE FREQUENCY CONTROL SYSTEM FOR ELECTRONIC MUSICALINSTRUMENTS Thomas J. George, North Hollywood, Calif., assignor toHammond Organ Company, Chicago, 111., a corporation of Delaware FiledSept. 25, 1962, Ser. No. 226,085 39 Claims. (Cl. 841.01)

This invention pertains in general to electronic musical instruments andmore particularly to electronic circuits and arrangements for producingnew and unusual musical effects using conventional keyboard instruments.

It is generally considered by serious musicians that the human voice isthe most beautiful of all musical instruments. For years, most pipeorgans and electronic organs have included a stop known as the voxhumana which is intended to simulate the human voice. However, it iswell-known that the effect, though usually pleasing, bears but littleresemblance to the human voice.

I have found that five major characteristics determine the sound of thehuman voice. These characteristics are tone quality, portamento, pitchrange, attack and release of the tones, and vibrato. When these fivecharacteristics are accurately simulated the artificial male voice iseasily distinguishable from the artificial female voice, and the realismis so striking that even experienced listeners may believe they arelistening to actual human voices.

Of the five characteristics, but little attention has heretofore beengiven to the importance of portamento and tone quality. It should bementioned here that although the term glissando has been commonly used,portamento is the correct musical term for describing the effect herereferred to, i.e., a glide in which all intervening frequencies areplayed. A glissando, in contrast, is a glide from note to note in whichdiscrete notes are successively played. Portamento is consideredpeculiar to the human voice, the violin, and the trombone and heretoforecould not be accomplished on any known conventional musical instrumentutilizing a keyboard.

To accurately imitate the human voice or a like instrument having .aportamento characteristic, with an electronic keyboard instrument, somemeans is needed for conveniently and accurately creating the portamentoeffect in response tothe conventional keying techniques which producethe discrete pitches. Prior efforts to provide instruments which produceportamento effects have not been very successful because the instrumentsrequire special equipment and playing techniques which are abnormal toconventional keyboards. Instruments utilizing such techniques include,for example, the Theremin and the instrument shown in the TrautweinPatent No. 2,141,231.

Furthermore, as pointed out, no known instrument is capable ofsimulating the tone quality or timbre of the human voice accurately.Acoustic analyses of the human voice indicate that there are threeidentifying attributes of the tone quality which are peculiar to thehuman voice when singing or speaking vowel sounds. These attributes are:(l) the first harmonic is nearly always lower in amplitude than thesecond harmonic or other low order harmonic; (2) a low frequency peakoccurs in the harmonic analysis of the voice tones approximately between500 and 900 cycles per second; and (3) a high frequency peak occur inthe harmonic analysis approximately between 2100 and 2900 cycles persecond. The three attributes have never been accomplished in combinationin any known conventional keyboard instrument. Of these threeattributes, the first is the most difficult to obtain electronically,because nearly all electronic oscillators which generate a complexwavetorm also generate a first harmonic of greater amplitude than allother har' monies.

In addition to the five above-mentioned characteristics, when the humanvoice is used as a solo musical instrument accompanied by one or moreother musical instruments, by design or otherwise, it usually assumesthe highest note (an accented melody note) for emphasis. Various devicesof the prior art are capable of accenting the highest note of any chordplayed, and known instruments have used'this feature. One such device(as used on pipe organs) is called the melody octave coupler. However,such devices require the player to always depress first the highest keyof any chord played and, likewise, to release it last when the chord isreleased. If the highest key is inadvertently released too soon, thenthe accented note drops down to the next lower note in the chord,producing an effect which is very unmusical and disturbing. Since askillful player will at times fail in this keying technique,arrangements based thereon have proved unsuitable for accenting themelody note. Various attempt-s to correct the difficulty inherent inknown devices have been made, but no real solution has been found.

Accordingly, it is an object of the invention to provide means foraccurately imitating the human voice on a conventional keyboardinstrument.

Another object of this invention is to provide means for accuratelyimitating the tone quality of a human voice by a conventional keyboardinstrument.

It is another object of the invention to provide means for playing noteswith a portamento effect on an electronic musical instrument whichemploys a conventional keyboard.

A further object of the present invention is to provide uniquearrangements for controlling tone quality and portamento effects of anelectronic musical instrument by means of a conventional keyboard.

Another object of the present invention is to provide a uniqueoscillator arrangement for furnishing variable two-frequency outputsignals, the oscillator having a memory circuit input for accomplishingportamento effects.

It is an additional object of the invention to provide an improvedarrangement for accenting the highest or lowest note of any chord playedon a conventional keyboard.

It is yet another object of the invention to provide simplified meansfor accomplishing various musical effects including means for actuatinga switch by the operation of any one or more of a plurality of playingkeys.

These and other objects are accomplished in accordance with the presentinvention by a unique circuit arrangement which includes an oscillatorcapable of producing signals which have a second harmonic content thatis greater in magnitude than the first harmonic content, and maytherefore be used to simulate the human voice. A novel memory circuit isprovided to supply an exponentiallyvarying control signal to theoscillator in response to keying changes for causing a portamentoeffect. The memory circuit is operated from a conventional keyboard by amechanical-electrical arrangement which provides a high-note effectwithout regard to fingering release.

The device of the present invention also includes a unique human-voiceoutput filter which allows it to imitate the singing human voice withstriking realism; The filter is such as to provide the twin peaks offrequency which are peculiar to the human voice. Other filtering meansare provided for furnishing alternative output signals for simulatingother portamento instruments.

A better understanding of the invention may be derived from thefollowing detailed description and the accompanying drawings in whichlike elements have like designations and in which:

FIG. 1 is a circuit diagram of one arrangement of a musical instrumentin accordance with the present invention;

FIG. 2 is an illustration of a waveform generated by the circuit of FIG.1;

FIG. 3 is an illustration of another waveform generated by the circuitof FIG. 1;

FIG. 4 is an illustration of still another waveform generated by thecircuit of FIG. 1;

FIG. 5 is a perspective drawing of a temperature compensated resistorfor use in the arrangement of FIG. 1;

FIG. 6 is a diagram illustrating the portamento elfect accomplished bythe arrangement of FIG. 1;

FIG. 7 is a perspective view of a key-actuated switch for use inproviding an accented melody note in accordance with the invention;

FIG. 8 is a side view of another key-actuated switch for use inproviding an accented melody note in accordance with the invention;

FIG. 9 is an end view of the key-actuated switch of FIG. 8;

FIG. 10 is a graphical illustration of the frequency response of afilter employed in accordance with the invention;

FIG. 11 is an illustration of the harmonic content of a particularsignal generated by the circuit of FIG. 1;

FIG. 12 is an illustration of the harmonic content of another particularsignal generated by the circuit of FIG. 1;

FIG. 13 is a diagram of a dual-voice simulating arrangement inaccordance with the invention;

FIG. 14 is a block diagram of a polyphonic musical instrument utilizingbalanced oscillators;

FIG. 15 is a circuit diagram of a stabilized oscillator which may beused in the invention; and

FIG. 16 is a circuit diagram of an alternative form of musicalinstrument in accordance with the invention utilizing areactance-controlled oscillator.

A preferred embodiment of the invention arranged in an electronic organcircuit is shown in FIG. 1 of the drawings. The functional components orblocks of the embodiment of FIG. 1 have been enclosed within dottedlines and labeled in order to facilitate an undertaking of the overallconcept of the invention. A keying arrange- -ment including aconventional keyboard provides input signals for operating the system.The conventional keyboard is mechanically coupled to operate a series ofselecting switches to make the appropriate connections for providinginput signals to a memory circuit. The selecting switches are connectedin a unique electrical-mechanical arrangement for accenting the highestnote of any chord played without the prior art problems of keying andrelease. The memory circuit provides a control bias which variesexponentially in response to the discrete signals provided by keyingchanges for achieving the glide between notes peculiar to the humanvoice and other portamento instruments.

The output of the memory circuit is furnished to an oscillator which isadvantageously adapted to provide two .output signals one octave apart,as required to simulate the tone quality of the human voice. Theoscillator is tunable, maintaining the octave frequency differencebetween signals, over a wide range depending on the variable inputcontrol signal supplied thereto from the memory circuit. The oscillatorhas an arrangement for adjusting the relative amplitudes of the chosenfrequencies thereby to better simulate the human male and female voicesor other selected musical instruments. The output signals from theoscillator are furnished to a gating circuit which selectively passesthe signals to a filtering circuit, adapted to selectively providesignals having the frequency peaks characteristic of the human voice orother portamento instruments. The signals from the filtering circuit arefurnished to an output circuit which includes an amplifier and a speakerin a well-known arrangement for producing sounds representing the inputsignals.

As the efiects accomplished by the arrangement are dependent on theproduction of two frequencies, the oscillator provides a convenientstarting point for a description of the invention. The oscillator is amodified form of multivibrator circuit which employs two triode electrontubes 10 and 11. The tubes 10 and 11 have their plates connected byresistors 12 and 13, respectively, to a source of positive potentialwhich is applied at a terminal 14. The plate of the tube 10 is coupledto the grid of the tube 11 by a capacitor 15, and the plate of the tube11 is coupled to the grid of the tube 10 by a coupling capacitor 16 andan adjustable capacitor 28 connected in parallel therewith. Gridresistors 17 and 18 connect the grids of the tubes 10 and 11,respectively, via a bias control lead 34 to the memory circuit.Resistors 22 and 23 connect the cathodes of the tubes 11) and 11,respectively, via a common cathode resistor 24 to ground potential. Thecommon cathode resistor 24 may advantageously be temperaturecompensated, for reasons to be explained hereinafter, by means of aheater winding 25 which may be energized by a low voltage sourceconnected across the terminals 26 and 27.

In operation, the oscillator functions to produce signals, thefrequencies of which are determined principally by the values of thegrid resistors 17 and 18, the values of the capacitors 15 and 16, andthe magnitude of the grid bias as controlled by the memory circuit viathe conductor 34. As will be explained, the grid bias furnished by thememory circuit varies with the input signal. As the bias decreases, thefrequency of oscillation is lowered, and as it increases, the frequencyof oscillation is raised. Using circuit values which will be givenlater, the frequency range of the oscillator of FIG. 1 may be made toextend .over three octaves while the output signal amplitude andwaveform remain substantially unchanged.

A significant feature of the oscillator of FIG. 1 is that, when it iscorrectly adjusted, it will generate, simultaneously, signals of twodiscrete frequencies which are one octave apart. To achieve thisperformance, the oscillator utilizes pairs of components which arebalanced within a tolerance of approximately ten percent. For example,the cathode resistors 22 and 23, the grid resistors 17 and 18, thecoupling capacitors 15 and 16, and the plate resistors 12 and 13 arebalanced. To further achieve the necessary balance, two adjustments areprovided for affecting 00th the resistance and the reactance of thecircuit. The variable capacitor 28 is connected in parallel with thecapacitor 16, and a high resistance potentiometer 29 is connected inparallel with the plate resistor 13 to furnish the adjustments.

With an oscilloscope (not shown) connected to the upper terminal 30 ofthe resistor 24, this balance can readily be observed. The waveforms ofFIGS. 2 and 3 illustrate conditions of unbalance and balance,respectively. As balance is approached, the diiference in height ofalternate peaks A and B diminishes; and at balance (as shown in FIG. 3),peaks A and B are exactly the same height. FIG. 2 is representative alsoof the waveform appearing at the cathode of the tube 11 which remainssubstantially unchanged, regardless of the balance adjustment. Thewaveform appearing at the plate of the tube 11 is represented in FIG. 4.This wave is approximately rectangular and is characteristic of amultivibrator circuit. The waveform appearing at a potentiometer contact32 is adjustable and, depending upon the position of the contact 32,this waveform may be varied between the limits indicated by thewaveforms of FIGS. 2 and 3.

The difference between the waveforms of FIG, 2 and FIG. 3 (those of thesignals at the terminals 30 and 31) monics of the oscillation frequencyin the signal at terminal 30 becomes more effective, and no difficultyis encountered in reducing the first harmonic, for example, to anamplitude more than 40 decibels below that of the second harmonic. Thesame action reduces all odd order harmonics simultaneously, so that atbalance the signal at the terminal 30 contains only even harmonics ofthe oscillation frequency. This, in effect, is a signal of twice theoscillation frequency having a harmonic family containing both odd andeven harmonics of twice the oscillation frequency. This is illustratedby the fact that there are twice as many cycles in the diagram of FIG. 3as in that of FIG. 2 or FIG. 4.

Such complete cancellation of the odd harmonics of the oscillationfrequency is not necessary for the simulation of the human voice. Thesignal obtainable at the contact 32, the harmonic content of which canbe varied, is therefore desirable for this purpose, for the secondharmonic of the signal may be adjusted to be higher in amplitude thanthe first harmonic to effectively simulate the human voice.

The balanced oscillator of FIG. 1 is frequency sensitive to changes involtages at the grids, the plates, and to some extent at the heaters ofthe tubes and 11. During the warm up period after the oscillator isfirst turned on, the frequency of oscillation will drift slightlyhigher, so that the instrument might be out of tune with any otherinstrument with which it is played. To compensate for this drift, theresistance of the cathode resistor 24 may be caused to increaseslightly. For example, the resistor 24 may comprise a temperaturesensitive resistor which is heated to slowly increase its resistanceduring the Warm up period. The heating may be accomplished by the heaterwinding 25 which may be constructed of resistance wire Wound around theresistor 24 and connected to a low voltage supply at a pair of terminals26 and 27, as shown in FIG. 5. The amount of heating required isdetermined from the physical size of the resistor 24, its positivetemperature coefficient and the rate of drift of the oscillator.Temperature compensation may also be employed with voltage dividerresistor 48 if desired, and in this case resistor 48 should have anegative temperature coefficient. Alternatively a temperaturecompensated resistor 48a may be connected in series with resistor 48 asshown in FIG. 13. These resistors may be constructed as shown in FIG. 5.It is desirable for the B+ voltage supplies at terminals 50 and 14 inthe figures to be regulated.

In operation, input signals are applied to the tubes 10 and 11 by thebias control coductor 34 which is connected to the plate of an electrontube 35 in the memory circuit. The plate of the tube 35 is alsoconnected by a plate resistor 36 to the source of potential at theterminal 14. The tube 35 has a cathode resistor 37 connected to groundand a cathode biasing resistor 38 connected to the source at theterminal 14. The grid of the tube 35 is connected to ground potential bya capacitor C39 and to a switch 41 by a parallel arrangement including aresistor 40 and a diode 53. The switch 41 is connected to a voltagedivider including serially connected resistors 47A-47K. A series of keyswitches 42-46 are arranged to connect the terminals between theresistors 47A-47K to terminals between variable resistors 49A-49L of asecond voltage divider, connected between ground potential and a sourceof positive potential at a terminal 59. As indicated by dashed lines, aconventional keyboard 52 has its playing keys arranged to operate thekey switches 42 to 46 by means of suitable mechanical linkages. Theoperation of any playing key and the corresponding one of the keyswitches 42-46 simultaneously closes the switch 41, the mechanicaldetails of which are given below.

As noted, the bias control lead 34 is connected to the plate of thememory circuit tube 35. Accordingly, if different direct currentvoltages are applied to the grid of the memory circuit tube 35, theplate voltage and the voltage on the conductor 34 will vary, controllingthe frequency of the oscillator in accordance with the magni- 6 tude ofthe voltages applied to the grids of the tubes 10 and 11.

When any key of keyboard 52 is operated to close a switch, for examplethe switch 42, the switch 41 is closed to provide a first potential .atthe grid of the tube 35 which charges the capacitor C39. Assuming thatthere are no substantial leakage currents fnorn grid to ground, anyvoltage charge upon capacitor C39 will remain, so long as the voltagedoes not exceed the positive cathode bias of tube 35. If good insulationis used on the wiring of the grid circuit, and if the capacitor C39 haslow leakage, as for example a good ceramic dielectric capacitor, thenthe charge will remain unchanged for an appreciable period of time; andfor that period of time the grid voltage which determines the frequencyof the oscillator will remain unchanged. Thus, it will be seen thatevery charge placed upon the capacitor C39, and the correspondingoscillation frequency, will be remembered by the circuit until adifferent charge is placed upon the capacitor C39.

When a different key is operated and a lower voltage is applied to thetube 35 through the resistor 40, an appreciable time will be requiredfor the voltage on capacitor C39 to reach the new value as determined bythe time contant of the resistor 40 and the capacitor C39. During thistime interval, the input signal provided to the oscillator will glidesmoothly from the old to the new value to produce a portamento effect,the final frequency of which is determined by the magnitude of the newcharging voltage.

Suppose that the playing key of the keyboard 52 linked to the switch 42is depressed, closing simultaneously the switches 41 and 42. The voltageappearing at the switch 42 from the voltage divider is applied throughall of the resistors 47A-47K in series and through the switch 41 tocharge the capacitor C39. The oscillator will generate the correspondingfrequency, which in this case is the lowest frequency of the keyboard.Now if the first key is released, and another key depressed, for examplethe key associated with the switch 46, then the switches 41 and 46 willsimultaneously be closed, and a lower voltage will be applied throughthe switch 41 to discharge the capacitor C39 gradually through theresistor 40 until its voltage reaches the lower level. The frequencywill glide up to the new note, and will remain there, even after theplaying key is released. If thereafter a lower key, for example the keylinked to the switch 45 is depressed, then a higher positive voltagewill be applied to the capacitor C39, and at this point the diode 53which is connected in parallel with the resistor 40, will be renderedconducting. The diode, as indicated, is poled so that it will conductcurrent toward the capacitor C39 but not away from it. Therefore, when apositive potential appears across the diode 53, the capacitor C39 ischarged through the diode 53 instead of the resistor 40, provided thatthe value of the resistor 40 is appreciably higher than the forwardresistance of the diode 53. This charges the capacitor C39 very rapidly,and little or no glide or portamento occurs.

Thus, when the new note played is lower in frequency than the last note,the capacitor C39 is charged through the diode 53 almostinstantaneously. When the new note is higher than the last note, thecapacitor C39 is gradually discharged through resistor 40, and there isa pleasing portamento. This action can easily be reversed by reversingthe polarity of the diode 53, but it has been found for most musicalapplications, that a portamento with rising frequency is much morepleasing than with falling frequency. If the; diode 53 is omitted therewill be portamento with either rising or falling frequency. Also if thevalue of the resistor 40 is made very low, there will be no portamentoin either direction, but always an instantaneous change in pitch.

According to another feature of the invention, the degree of theportamento effect may be varied by .arranging a variable capacitor C150in parallel with the resistor 40-. The connection may be made by aswitch 151. Depending on the value chosen for the capacitor C150, thetuning voltage may be caused to move instantaneously to a chosen pointbetween the old .and new values before the portamento effect begins. Forexample, as shown in FIG. 6, if the value of the capacitor C150 is setto equal that of the capacitor C39, the tuning voltage moves to themidpoint between the old and new values; and then the glide to the newvalue begins. The effect produced is more natural in the simulation ofcertain instruments. Examples of the effect of the capacitor C150 areshown in FIG. 6 where the voltage changes on the capacitor C39 forvarious values of the capacitor C150 are illustrated.

The variable resistors 49A-49L function as the tuning controls, and eachmay be of a relatively low value, such as 500 ohms. While only fivetuning resistors 49 are shown, any number of separate tuning resistorsand key switches may be used, depending upon the keyboard range desired,with a range of from two to three octaves being adequate. The resistor48 has a unique current limiting function which greatly simplifies thetuning of the instrument. If the resistor 48 has a resistance value notless than three or four times the total resistance value of all of thetuning resistors 49A-49L, the small tuning adjustments of the resistors49A-49L will not appreciably affect the current through the voltagedivider because the resistor 48 limits the current flow. It is thuspossible to tune individual notes without appreciably changing thetuning of other higher notes of the instrument. However, if a number ofnotes are to be tuned, the notes should .be tuned in sequence startingwith the highest notes to be tuned, because all lower notes will beaffected. One advantage of this arrangement is that the resistor 49Lwhich interconnects switch 46 and ground serves as a master tuningcontrol. By tuning the resistor 49L, all notes may be moved up or downsimultaneously to bring the device into tune with some other instrumentwhich is not so easily tuned.

The resistors 47A-47K should each have a resistance value which isapproximately ten to fifteen times the resistance of each resistor49A-49L. If this switching arrangement is used as a part of a polyphonicmusical instrument, then several of the playing keys may be depressed atone time, When this is done, it is important that the tuning of theindividual solo notes should not be disturbed. If for example, the keyswitches 42 and 46 are closed simultaneously, then all the resistors47A-47K between the two key switches will be connected in parallel withall of the resistors 49A49K. If resistors 49A- 49L are eachapproximately 500 ohms, then resistors 47A-47K should be not less than5000 ohms. The resistor 40 may be one megohm or larger, depending uponthe rate of portamento desired.

Another point of importance in relation to use of the invention with apolyphonic instrument is the arrangement which selects the highest orlowest note when several keys are played simultaneously. A conductor 54connects the switch 41 to the switch 46 as shown, or, alternatively, tothe lowest frequency switch 42. When the conductor 54 is connected tothe switch 46, if several keys are depressed, the highest note will haveprecedence. If lead 54 is connected to switch 42, then the lowest notein any chord will have precedence. In this way either the highest orlowest note of any chord may be the solo voice. This is a very usefulfeature, because prominence can be given the melody, which is usuallythe highest note of any chord. However, the feature is also useful foraccenting the lowest note of any chord played in providing bassaccompaniment. In a small electronic organ, the bass part can beprovided in this way very economically. An alternative circuit for thispurpose is described hereinafter.

In accordance with one aspect of the present invention, the difficultyof prior art arrangements relating to the inadvertent release of thehighest key of a chord is solved by the operation of the controlmechanism for the switch 41. This mechanism is such that if severalnotes of a chord are depressed, the solo device will sound the highestnote, as previously described. If the highest key is inadvertentlyreleased, while one or more lower keys remain operated, the switch 41opens immediately, even before the tuning switch 42-46 is opened, sothat the voltage on the capacitor C39 remains unchanged and theoscillator continues at the same frequency. The only way to close theswitch 41 again is to play either the same or a different key.

To accomplish the foregoing, the switch 41 is of special design. Thedetails of two suitable forms for its construction are shown in theperspective drawing of FIG. 7 and the views of FIGS. 8 and 9. In FIG. 7the rear ends of four playing keys 89a89d of the keyboard 52 are shown.The key 8% is indicated as depressed while the keys 89a, 89c and 89d arein normal position. A flexible cord 91, such as braided wire or dialcord, is mounted above the top surfaces of all keys 89 and is stretchedbetween a mounting post 92 and a slide rod 93. Rigid stop members 94 aremounted between the keys 89 immediately above the flexible cord 91 sothat the cord 91 touches the upper surfaces of the keys and the lowersurfaces of the stop members 94. The slide rod 93 of friction switch 41is loosely mounted in a pair of bearing blocks 95a and b so that it isfree to move either to the left or the right. A retractile spring 96,anchored to a post 97, pulls the slide rod 93 to the right, thusmaintaining a tension upon the flexible cord 91. A spring contact member98, which may be made of spring silver wire, is mounted upon a metalsupport post 99. The contact member 98 passes through a friction blockwhich is loosely mounted upon the slide rod 93. The friction block 100and the bearing blocks 95 may be constructed from a suitable smoothbearing material such as nylon. Two electrical contact posts 101 and102, are vertically mounted close to, but not normally touching, thespring contact member 98. A pair of connecting leads 54 serve to connectthe switch 41 with the keying and memory circuits shown in FIG. 1. Thespring contact member 98 may be tensioned downwardly so that it urgesthe friction block 100 against the slide rod 93, causing frictiontherebetween. The spring contact member 98 is not however, tensionedeither to left or right, and has little or no tendency to touch eitherof the contact posts 101 or 102.

Upon the operation of any playing key, such as 8%, the inner end of thekey rises, pulling the cord 91 upwardly as indicated. The restrainingaction of the two stop members 94 on each side of the key, causes thecord 91 to be drawn tight, thus pulling the slide rod 93 to the left.The movement of the slide rod 93 moves the friction block 100 to theleft, causing the contact member 98 to move to the left and makeelectrical connection with the contact post 101. This connection will bemaintained until the key is released, at which time the spring 96 willdraw the slide rod 93, the friction block 100, and the contact member 98to the right, thus breaking the connection with the contact post 101. Ifwhile key 89b is operated, one or more additional keys are operated, theflexible cord 91 will be pulled still more, causing the slide rod 93 tomove still farther to the left. But since the contact member 98 isalready pressing against the post 101, the slide rod 93 moves within thefriction block 100. Due to the friction between the slide rod 93 and thefriction block 100, the contact 98 is held in firm engagement with thepost 101 during this movement.

If one or all of the keys are released, the spring 96 draws the sliderod 93 to the right. The contact member 98 is disengaged from thecontact post 101 and moves against the post 102 which acts as a stop toprevent the friction block 100 from following the slide rod 93 for morethan a very short distance in its movement to the right. The actualspacing between the contact posts 101 and 102 is very small, onlyslightly more than the thickness of the contact member 98, so thatalthough the movement of the slide rod may be substantial if a number ofkeys is played, yet the movement of the friction block 100 and thecontact member 98 is always very small. Thus, when a key 89 is nextoperated, the contact member 98 moves immediately to the left, upon thefirst slight motion of the flexible cord 91. On the other hand, when anykey 89 is released, the first slight motion of the cord 91 causes thecontact member 98 to break electrical contact with the post 101, eventhough other keys may simultaneously remain operated. Thus, it will beseen that the switch 41 makes contact if one or more keys are operated,but what is more important, it breaks contact instantly upon the releaseof any key, even though other keys are still held depressed.

The friction switch mechanism of FIG. 7 thus makes it possible to obtainmelody note accent with a polyphonic instrument, without the necessityof learning new and difiicult playing techniques. The friction switch 41could of course be controlled by some other mechanical device orelectrical device common to all the playing keys, instead of theflexible cord shown in the figure. A sliding or rotating rod forexample, could be substituted for the cord. It should be noted thatwhere the invention is to be used only as a solo instrument, and not inconjunction with a polyphonic instrument, the switch 41 is not required,since in this case only one key at a time will normally be played.

In FIGS. 8 and 9 is shown another arrangement for operating the switch41 of FIG. 7, FIG. 8 being a side view and FIG. 9 a rear view of thekeys. The key 89 has a pair of intermeshed nylon pulleys 160 and 161mounted to its rear surface which establish a slot 162 for carrying theflexible cord 91.

The arrangement operates substantially like that shown in FIG. 7 tooperate the switch 41 except that the friction of operation attributableto the movement of the cord 91 is substantially reduced. As a key isdepressed, the pulleys 160 and 161 mounted thereto raise the cord 91 andcause the switch 41 to close. As any key is released, the cord 91 islowered and the switch 41 opens.

It will be understood in the appended claims that where the invention isused in conjunction with a polyphonic musical instrument having agreater keyboard range than that normally employed by the invention,that the invention may be adapted to be operated by only a selectedportion of the entire keyboard. It will be further understood that theterm friction switch refers to the switch 41 shown in FIG. 7.

Referring now to the gating section of FIG. 1, an electron tube 55 isarranged to gate the output signals from the oscillator. Since theoscillator, although generating different frequencies, is in continuousoscillation, it is necessary that means, controlled by the playing keys,be provided to selectively transmit the signal to the output system onlywhen keys are depressed to play selected notes. The gating tube 55 has aplate resistor 56 connected to the voltage source at the terminal 14. Avoltage divider including the resistors 57 and 58, connected in seriesbetween the terminal 14 and ground is arranged to bias the cathode ofthe tube 55 at cutoff. The grid of the tube 55 is connected to theswitch 59 by serially arranged resistors 60 and 61. The switch 59 is inturn connected between the resistors 62 and 63, of a voltage dividerarranged between the source of positive potential at a terminal 51 andground. When the switch 59 is open, the tube 55 is cut OE; and whenclosed, the tube 55 is conducting. A timing capacitor 64 is connectedfrom the junction of the resistors 60 and 61 to ground for controllingthe attack (the time required for tube 55 to conduct) and release (thetime required for tube 55 to cease conducting) of the tones. Theresistor 60 affects the attack, and the resistor 65, connected betweenthe grid of the tube 55 and ground, afiects the release of the tones.The resistor 61 is a grid coupling resistor.

A switch 66 is arranged to selectively connect the grid of the gatingtube 55 to either a switch point 67 or a switch point 69. When connectedto the point 67, a signal from the potentiometer 23 is passed to thegrid of tube 55 by a capacitor 68. When the switch 66 is connected tothe point 69, a signal from the plate of the oscillator tube 11 ispassed by a direct current blocking capacitor 70 to the grid of thegating tube 55. The operation of the switch 66 and the adjustment of thepotentiometer 23 allow the selection of any of the waveforms shown inFIGS. 2, 3 and 4.

The signal output of the gating tube 55 is passed by a capacitor 71 to avoicing selector switch 72. When the switch 72 is connected to a point73, the signal is passed by a resistor 76 to an output amplifier 78 andthence to a speaker 79. When the switch 72 is connected to a point 74,the signal is passed to the output amplifier through a capacitor 80,which functions as a high pass filter to attenuate the lower harmonicsin the tone for the simulation of violin tones.

When the switch 72 is connected to a point 75, the signal path to thespeaker 79 is through a filter which produces the two response peaksnecessary to the accurate simulation of the tone quality of the humanvoice. As previously mentioned the two frequency peaks in the humanvoice are an important identifying characteristic. The frequencyresponse curve of this filter is shown in FIG. 10, and it will be seenthat it meets this requirement. The filter comprises a first sectionincluding an inductor 81 connected in series between the point and thespeaker 79, and a pair of shunt capacitors 85 and 86 which determinesthe gently rising curve up to about 900 cycles per second and the fairlyrapid cut otf above approximately 1000 cycles per second. The filteralso comprises a second section including an inductor 82 and capacitor83 in series which provides a band pass filter with a response peak atapproximately 2300 cycles per second. As indicated, this latter peakshould be approximately 6 or 8 decibels lower than the peak at 900cycles per second.

As indicated by the dashed lines, the operation of any one of theswitches 42 to 46 in response to the depression of a key is accompaniedby the simultaneous operation of the gate switch 59. Upon operation ofany key, the gate circuit is operated by the closure of the gate switch59; and the oscillator signal is passed to the output system.

FIG. 11 is a harmonic analysis of an artificial male voice produced bythe arrangement of this invention, corresponding to the signal appearingat the input to the amplifier 78. The frequency of the tone isapproximately cycles per second; and it will be observed that the firstharmonic, at 100 cycles per second is considerably lower in amplitudethan the second harmonic. In fact, the second harmonic is the strongestof the entire series. This harmonic relationship is necessary to imitateaccurately the male voice, and it is obtained as previously describedfrom the balanced oscillator, by selective adjustment of the contact 32of the potentiometer 23. It will be seen that above the second harmonic,the amplitudes of succeeding higher harmonics drop 01f rapidly, and thenrise to a peak at approximately 2300 cycles per second following thegeneral shape of the curve of FIG. 10.

FIG. 12 is an analysis of an artifical female voice of a frequency ofapproximately 200 cycles per second which may be produced in accordancewith the invention. Here the amplitude of the first harmonic is almostas great as that of the second harmonic. This difference between therelative strengths of the first and second harmonics is an importantdistinguishing feature of the human male and female voices and iscontrolled in the arrangement of FIG. 1 by the potentiometer 23. Thedrop off of harmonic amplitudes above 1000 cycles per second isapproximately the same as in FIG. 11, with a peakalso in the region of2300 cycles per second.

Examples of harmonic analyses of human voices, il lustrated on page 230of Musical Acoustics by Culver, published by McGraw-Hill Publishing Co.in 1956, show their similarity to the analyses of FIGS. 11 and 12. Itshould be noted that the actual numbers of the harmonies which fallwithin the secondary peak at 2300 cycles per second is of littleimportance, so long as the peak itself is in the neighborhood of 2300cycles per second, and the analyses indicate the general distributionrather than the actual numbers of harmonics. It may be found that thispeak, for the female voice, should be slightly higher in frequency thanfor the male voice.

It should be noted that two voice simulating arrangements, one tuned tosimulate a male voice and the other to simulate a female voice, may beoperated in tandem to provide a duet elfect. Such an arrangement isshown in FIG. 13, for example. The two memory circuits connect the tubes35F and 35M of the female and male voice channels, respectively, to theopposite ends of the resistor 47 so that the tubes 35F and 35M receivethe appropriate input signals for accenting the highest and lowest notesplayed to produce the duet effect. Excepting the common switchingsystem, the two channels are entirely separated, and for best spatialseparation of the two voices, each channel has its own output system.The details of each channel of the arrangement are as shown in FIG. 1 sono further description thereof is believed to be required.

In normal operation of the arrangement of FIG. 1, the oscillator is incontinuous operation. With no key depressed, the gating tube 55 is inthe cut off condition; and no signal reaches the amplifier. Now, supposethat the lowest note of the keyboard 52 is depressed; the switch 42closes, and simultaneously the switches 41 and 59 close. The oscillatoris tuned to the lowest frequency, and at the same time the positivekeying voltage through the switch 59 begins to charge the capacitor 64and to render the gating tube 55 conducting. A signal appears at theoutput of the gate tube 55 and speaker 79. The attack will be gradualbecause of the delaying action of the attack resistor 60 and thecapacitor 64. Now, suppose that the highest note is played. The gatingtube 55 remains conducting; and in the memory circuit, the lowerpositive voltage from the switch 46 slowly discharges the capacitor 39through the resistor 40 to the lower positive tuning voltagecorresponding to that note. The frequency glides smoothly from the lowernote to the higher note. Now, if the key is released opening theswitches 41 and 59, the voltage on the capacitor 39 and the frequency ofoscillation remain the same. The release control capacitor 64 slowlydischarges through the resistors 61 and 65, in series; and the gatingtube 55 gradually becomes nonconducting, producing smooth and gradualrelease of the tone. If the capacitor 64 is made quite large, therelease of the tone will be quite slow; and the effect of a sustain willresult. Also, if resistor 60 of the gate circuit is quite small whilethe capacitor 64 is large, the opening of the gate circuit will bepractically instantaneous, and the release of the tones quite slow;resulting in a percussion effect. If vibrato is desired, it may veryeasily be obtained by applying a low frequency signal to the cathode ofthe tube 35. This signal can usually be obtained from the vibratooscillator of the organ with which the device is to be used.

The switch 88 in the human voice filter is arranged to connect anadditional capacitor 87 across the shunt capacitor 86. The switch 88 isnormally closed. The dashed lines indicate that this switch is alsocontrolled by the keyboard 52; and mechanical means, not shown, operateto open the switch 88 whenever a playing key in the upper octave of thekeyboard is depressed. The reason for this action is as follows. When asinger has been singing a low note, and then glides up to a high note,there is a seeming slight change in the frequency response of theacoustic filters formed by the mouth and throat, perhaps caused byopening the mouth slightly more for the higher notes. To simulate thiseffect, opening of the switch 88 raises the cut off point of the filtercurve of FIG. 10 slightly, say from 900 cycles per second to about 1000cycles per second, when playing notes in the high octave of theinstrument, so that the realism of the human voice effect is stillfurther enhanced. The effect is equally useful with both male and femalevoice effects.

It has been mentioned that the solo device of this disclosure may beemployed to advantage in conjunction with a polyphonic musicalinstrument, and such an instrument is briefly described as follows.Because the balanced oscillator of FIG. 1 generates simultaneously twodiscrete frequencies one octave apart, it is possible in accordance withanother aspect of the invention to provide a polyphonic musicalinstrument which employs half the number of oscillators usuallynecessary, by sharing each balanced oscillator between two keys, oneoctave apart. A substantial economy can thereby be realized. FIG. 14 isa block diagram of such an instrument, which employs a four octavekeyboard 104. The block contains twelve balanced oscillators as in FIG.1, and the block 106 contains another twelve balanced oscillators. Theoscillator of FIG. 15 may also be used here and is described later. Thetwelve oscillators of the block 105 are tuned to the twelve chromaticnotes of the lowest octave of the instrument, and the oscillators of theblock 106 are tuned to the twelve notes of the octave which is twooctaves above the lowest octave. Signal leads 107 join the outputterminals 31 (FIG. 15) of the oscillators to the key switches (notshown) of the lowest octave of playing keys. A common output bus 108carries the combined signals from the keys to an output amplifier 109and a speaker 110. Details of the switching circuit are not shown, asthey are well known in the art. Twelve signal leads 111 join the outputterminals 30 (FIG. 15) to the switches of the second octave of theinstrument. Thus signal frequencies for two octaves are obtained fromonly twelve balanced oscillators.

In like manner, the oscillators in block 106 are wired to the keyswitches of the third and fourth octaves of the keyboard, the leads 112connecting to oscillator terminals 31, and the leads 113 connecting tothe oscillator terminals 30. By this means, considerable economy ispossible in the design of an electronic organ. Although this arrangementis a form of shared oscillator organ, yet the system does not have thelimitations so common in shared oscillator organs of the prior art,because in the present invention any combination of keys can be playedsimultaneously.

To improve the frequency stability of the balanced oscillator of FIG. 1when used at one frequency only, a center tapped inductor may besubstituted for the two plate resistors 12 and 13. FIG. 15 shows acircuit which employs such an inductor 114. A center tap 116 of theinductor 114 is connected to the terminal 14, and the two terminals 117and 118 of the inductor 114 are connected to the plates of the tubes 10and 11. The inductor 114 is in parallel with a tuning capacitor whichcontrols the frequency of oscillation. As in FIG. 1 the fundamentalfrequency signal will appear at the terminal 31, and the frequency anoctave above will appear at terminal 30. Since there are no plateresistors in the circuit of FIG. 15, a balance control potentiometer 29is connected in parallel with the cathode resistor 23 and serves thesame balancing function as in FIG. 1. Balancing capacitor 28 isconnected in parallel with the capacitor 16 as in FIG. 1. The waveformsof the signals at terminals 30 and 31 are an octave apart in fundamentalfrequency and are of complex waveform as in FIG. 1. The waveform of thesignal at terminal 33 is a sine wave of the frequency of the signal atthe ter- 13 'rninal 31. The grid voltage adjustment 20 of potentiometer19 is no longer a major factor in controlling the frequency ofoscillation but is useful as a fine tuning control. The common cathoderesistor 24 serves the same function as before but may be used withoutthe frequency compensating heater 25. This balanced oscillator' is verystable in frequency and can be used to advantage in the instrument ofFIG. 14, when substituted directly for the oscillator of FIG. 1.

Another useful form of the invention is shown in FIG. 16. An L-Coscillator 119 using the conventional Hartley circuit is arranged to betuned over a range of frequencies in a manner similar to the oscillatorof FIG. 1. The oscillator 119 comprises a triode tube 120, a tappedinductor 121, a parallel tuning capacitor 122, a grid capacitor 123, agrid resistor 124, a plate resistor 125 and a plate shunt resistor 126.A resistor 132 interconnects the cathode of the tube 120 and the tap onthe inductor 12L Output signals may selectively be taken from theoscillator'plate, the cathode, or from the inductor. The oscillator 119is tuned by means of a reactance tube 128 and a capacitor 129, as iswell known in the art. The reactance tube 128 has a plate resistor 130connected to the terminal 14, and the tuning capacitor 129 interconnectsthe plate of the reactance tube 128- and the grid end of the oscillatortuning inductor 121. The grid of the'tube connects directly to the samepoint on the inductor 121.

A memory tube 35 and associated switching circuit are used as in thecircuit of FIG. 1, the keyboard having been omitted from the drawing ofFIG. 16. The plate of the tube 35 connects directly to the terminal 14.The tube functions as a cathode follower, having a cathode resistor 131common with the reactance tube 128. The tube 35.0perates to vary thecathode bias of the reactance tube 128 which in turn controls thefrequency of the Hartley oscillator by causing an apparent variation ofthe tuning capacitor 129. The key switches 42 to 46, in conjunction withthe voltage divider resistors 49A-49L and resistor 48, selectivelycontrol the grid bias on the tube 35, in the manner previouslydescribed, to tune the oscillator 119 to the desired musical pitches.The relative values of capacitors 122 and 129 control the frequencyrange of the oscillator. When they are about equal the frequency rangeis one octave. When capacitor 129 ismade larger and capacitor 122smaller the frequency range increases. Capacitor 122 may be omittedentirely for maximum range.

The Hartley oscillator has one advantage, for certain applications, overthe balanced oscillator circuit of FIG. 1 because it will deliversimultaneously a sine wave and choice of two complex waves. The sinewave, which is not obtainable directly from the balanced oscillator, isvery useful in simulating certain kinds of musical effects such asflutes, and percussive effects such as chimes, vibra-harp, bells, etc.

The circuit of FIG. 16 also includes a gating tube 55 which is employedfor the same purpose'as in the circuit of FIG. 1. Additional components,designated by the same characters as used in FIG. 1, have similarfunctions. A blocking capacitor 127 interconnects the grid of the gatetube 55 and a selector switch 140. When the selector switch 140 isconnected to a switch point 137, the signal from the oscillator inductor121 is transmitted to the gate tube 55. This signal is substantially asine wave. When the switch is on a point 138, a complex wave from thecathode is transmitted to the gate tube 55. When the switch is connectedto a point 139, a

complex wave from the plate is transmitted to the gate tube 55. The tube55, as previously mentioned, is normally at cathode bias cut off. Aswitch 133 (which, as indicated by the dashed line, is operatedsimultaneously with any of the keying switches) is normally connected toback contact 134. A normally open front contact 135 is connected to theattack resistor 60. With the switch 133 in the normal position, astorage capacitor 136 is charged to a positive keying potential. Thepotential is determined by the relative values of resistors 62 and 63,arranged in series between the terminal 14 and ground. When the switch133 is operate dto connect with the front contact 135, the positivecharge on the capacitor 136 is transmitted through the attack resistor60 to a normally discharged timing capacitor 64 and to the grid of thegate tube 55. The gate tube 55 opens and transmits the oscillator signalthrough tone color filters 137 to the output amplifier 78 and thespeaker 79. As the charges on the capacitors 136 and 64 are dissipatedthrough the serial resistors 60, 61 and 65, the gain of the gate tube 55gradually decreases; and the tone from the speaker dies away, producinga percussive musical effect. When the switch 133 is restored to normal,the capacitor 136 is charged again for the next note to be played.

In the memory circuit of FIG. 16, the charging resistor 40 for capacitor39 may be made relatively small, approximately 33,000 ohms. Frequencychanges of the oscillator 119 with keying will therefore be practicallyinstantaneous.

The circuit of FIG. 16 is very useful as a generator of bass pedal notesfor an organ and can be manufactured inexpensively. Since two pedalnotes are almost never played together, a solo pedal circuit is quitepractical. Percussive pedal effects are very useful for rhythm playingin popular music. Also pedal sustain is very useful as it provides apseudo reverberation effect, which makes it easier to play the organ,especially for inexpert players. The gate keying circuit of FIG. 1 is asustain circuit which maintains any note played as long as the key isheld, which then dies away gradually when the key is released. The gatekeying circuit of FIG. 16 is a percussion circuit. The note dies awayafter the note is struck, whether or not the key is held depressed, andthe memory circuit holds the oscillator on the last frequency playedduring the die away period. The capacitor 64 should be large enough toprovide an appreciable period even though switch 133 is released.Usufollows:

Resistor 12 ohms 33, 000 Resistor 13 do 33, 000 Source of potential atterminal 14 volts Resistor 15 rnicrofarad- .002 Resistor 16 microfarad.0017 Resistor 17 ohms 560, 000 Resistor 18 do 560, 000 Resistor 19 do250, 000 Resistor 21 do 100, 000 Resistor 22 do 3, 300 Resistor 23 do 3,300 Resistor 24 do 100, 000 Capacitor 28 microfarad .0005 Resistor 29ohms 250, 000 Resistor 36 d0 100,000 Resistor 37 do 22, 000 Resistor 38do 330, 000 Capacitor 39 microfarad .01 Resistor 40 megohms 1 to 5Resistor 47 ohms 5, 000 Resistor 48 do 42, 000 Thermister 48a do 75 to750 Resistor 49 do 500 Source of potential at terminal 50 volts 150 15Diode 53 Type 1T1 rectifier Resistor 56 ohms 560, 000 Resistor 57 do220, 000 Resistor 58 do 33, 000 Resistor 60 do 100, 000 Resistor 61 do330, 000 Resistor 62 do 120, 000 Resistor 63 do 710, 000 Capacitor 64microfarad .25 Resistor 65 megohms 2.4 Capacitor 68 microfarad .01Capacitor 70 do .01 Capacitor 71 do .01 Resistor 76 ohms 560, 000Capacitor 80 microfarads .001 Inductor 81 lhenrys 14 Inductor 82 do 17Capacitor 83 microfarad (female) .0002 Capacitor 83 microfarad (male).0005 Resistor 84 hms 330, 000 Capacitor 85 rnicrofarad .002 Capacitor86 do .002 Capacitor 87 microfarad 0005 Inductor 114- henrys Capacitor115 microfarad .013 Inductor 121 henrys 100 Capacitor 122 microfarad.017 Capacitor 123 microfarad .022 Resistor 124 ohms 330, 000 Resistor125 ohms 56,000 Resistor 126 do 27, 000 Capacitor 127 microfarad .05Capacitor 129 do .019 Resistor 130 ohms 330, 000 Resistor 131 do 33, 000Resistor 132 do 6, 800 Capacitor 136 microfarad .25 Capacitor 150 doZero to .1

All tubes shown are 12AU7 tubes, excepting 10 and 11 which are 12AX7tubes. It should be stressed that the vacuum tubes in the circuits shownin the drawings might in some cases be replaced by transistors, Withoutdeparting from the spirit of the invention.

Although there have been described above specific arrangements of organcircuits for the purpose of illustrating the manner in which theinvention may be used to advantage, it will be appreciated that theinvention is not limited thereto. Accordingly, any and allmodifications, variations or equivalent arrangements falling within thescope of the annexed claims should be con sidered to be a part of theinvention.

What is claimed is:

1. An electronic musical instrument comprising a variable frequency tonegenerator having a control terminal, a keyboard, and means for applyingsignals to the control terminal to change the frequency of operation ofthe generator in response to the manipulation of the keyboard, saidsignal applying means including unilaterally conductive means fordecreasing the frequency in discrete intervals and means for imparting aportamentoeffect to increases in the frequency of operation of thegenerator.

2. An electronic musical instrument comprising a voltage controlledvariable frequency oscillator, means for providing discrete voltageinput signals for controlling the frequency of the oscillator and meansfor selectively coupling said discrete input signals to control thefrequency of operation of the oscillator, said coupling means includingafirst conductive path for gradually changing the control voltageapplied to said oscillator to vary the frequency of the oscillator witha portamento effect in response to changes in discrete input signals ina first sense and a second conductive path for changing the controlvoltage applied to said oscillator by discrete intervals to 16. vary thefrequency of ope-ration of the oscillator by discrete intervals inresponse to changes in discrete input signals in a second sense.

3. An organ circuit comprising a variable oscillator having input andoutput terminals; selection means for furnishing a plurality of discreteinput signals; and means for operating the oscillator at frequenciesdependent upon the input signals furnished, said oscillator operatingmeans comprising means for providing an-exponentially varying signal tothe input terminal of the oscillator in response to changes in onedirection in the discrete input signals provided and for providing adiscrete change in the signal to the input terminal in response tochanges in the other direction in the discrete input signals provided. I

4. A variable tone frequency generator comprising a multifrequ'encyoscillator having input means, output means, and means for generating acomplex output signal including a first frequency and a second harmonicof said first 'frequency of greater amplitude than said first frequency;a plurality of mechanically operated means for furnishing a plurality ofdiscrete input signals; means connected to said input means andoperative responsive to individual ones of the discrete input signalsfor varying the frequencies of operation of the oscillator, saidlast-mentioned means comprising a memory circuit connected to saidplurality of mechanically operated means; a frequency filtering meansfor selectively attenuating certain frequencies in accordance with adesired tone quality and means for selectively connecting the frequencyfiltering means to the output means of the oscillator.

5. A tone generator comprising an oscillator having input and outputterminals; utilization means connected to the output terminal of theoscillator; means for providing a plurality of discrete input signals,each of said plurality being operable to provide a particular discreteinput signal representative of a given tone and being operable withothers of said plurality for providing a combination of discrete inputsignals representative of a different tone; a memory circuit coupled tothe input terminal of the oscillator, said memory circuit comprising anamplifier having an input terminal and an output terminal connected tothe input terminal of the oscillator, a current limiting resistor forproviding said input signals therethrough to the input terminal of saidamplifier, and a timing capactor connected to shunt the input terminalof the amplifier for providing exponentially varying signals thereto inresponse to changes in the input signals; and a switch means responsiveto the operation of any of said plurality of means for selectivelycoupling said input signals to' said memory circuit and for selectivelyuncoupling all of said plurality of means from said memory circuitwhenever the operation of any one of a number of simultaneously operatedones of said plurality of means is terminated so that the signalprovided by said timing capacitor is maintained substantially unchangeduntil a subsequent operation of one of said plurality of means.

6. A tone generator ras defined in claim 5 further comprising a diodeconnected in parallel with the resistor.

7. A tone generator as defined in claim 6 further comprising a capacitorconnected in parallel with the resistor.

8. A multi'frequency tone generator comprising a multivibrator includingfirst and second vacuum tubes each having a cathode, a plate and atleast one grid, a pair of balanced capacitors each of which is connectedbetween the plate of one of said tubes and the grid of the other of siadtubes, a pair of balanced grid resistors, a pair of balanced cathoderesistors, a thermally-sensitive resistor connected in common to thecathode resistors, means for increasing the ambient temperature of thethermally-sensitive resistor, and means for biasing the multivibratorcircuit; and input circuit for varying the potentials fiu-rnished thegrid resistors of the multivibrator comprising an input vacuum tubehaving a plate coupled to said grid resistors, means for biasing theinput vacuum tube, and means for applying input signals between the gridand cathode of the input vacuum tube including a capacitor connectedtherebetween and an input resistor connected to the grid of the inputtube; an arrangement for furnishing signals to the input circuitcomprising a D.C. potential source, a plurality of variable resistorscoupled in series across the DC, potential source, a voltage dividercircuit having a plurality of electrical input connections distributedat approximately equal intervlals therealong, means for selectivelyconnecting terminals between said variable resistors to the inputconnections of the voltage divider, and switching 'rneans operative inresponse to the connection of the input connections of the voltagedivider to one of said terminals for connecting the voltage divider tothe input resistor of the input vacuum tube and operative in response tothe release of any connection between the voltage divider and one ofsaid terminals for disconnecting the voltage divider from the inputresistor; a gating circuit comprising a vacuum tube biased at cut off,means responsive to the connection of the voltage divider to one of saidterminals for biasing the vacuum tube of the gating circuit in theoperating condition, means for selectively applying a signal from themultivibrator to the input of the vacuum tube of the gating circuit; andan output arrangement comprising a high-pass filter, a resistive outputchannel, and a combination filter having first and second frequencypeaks at predetermined frequency points, said combination filterincluding means for selectively retuning the combination filter so thatthe frequency point of one of said peaks is varied in response to theconnection of predetermined ones of said terminals to said voltagedivider, and means :for selectively connecting the output of the gatingcircuit to one of said filters or to said output channel.

9. A multirrequency tone generator circuit as defined in claim 8 whereinthe gating circuit includes means for causing changes in the biasapplied to the vacuum tube of the gating circuit to take placeexponentially.

10. A multitone generating circuit comprising a multivibrator circuithaving first and second active elements and a resistor connected incommon with said first and second elements; an arrangement for applyingvariable input signals to the multivibrator circuit comprising a Voltagesensitive amplifier circuit having input means comprising a voltagestorage arrangement, a source of direct current potential, a firstvoltage divider connected across said source and having a plurality ofsubstantially evenly spaced points for connection thereto, a secondvoltage divider having a plurality of substantially evenly spaced pointsfor connection thereto, means for selectively con necting a point on thefirst voltage divider to 3. corresponding point on the second voltagedivider and means for selectively connecting the second voltage dividerto the voltage storage arrangement; a frequency filtering circuit; meansfor selectively sampling signals appearing at various discrete points ofthe multivibrator circuit and furnishing indications representativethereof to the filtering circuit; and output means connected to thefiltering circuit.

11. A multitone generating circuit as in claim 10 wherein the means forconnecting the second potentiometer to the voltage storage arrangementcomprises a switch operated in response to the connection of any pointof the first voltage divider to any point of the second voltage divider,said switch comprising means for connecting the second voltage dividerin the input storage arrangement immediately upon an initial connectionand for opening said switch immediately upon the opening of anyconnection.

12. A multitone generating circuit as in claim 11 wherein the switchcomprises a flexible cord connected to a first stationary point, a rodconnected to the flexible cord, a

spring connected between a second stationary point and the rod, apluraltiy of mechanical means for moving the flexible cord perpendicularto its length in response to the movement of individual keys of akeyboard, a first switch contact fixedly mounted adjacent the rod, asecond switch contact of a flexible material mounted to engage the firstswitch contact, and a block arranged in sliding friction contact withthe rod and engaging the second switch contact for movement with therod.

13. In a polyphonic musical instrument, a, solo device for accenting thehighest note of any plurality of notes simultaneously played including avoltage sensitive variable frequency electronic generator having acontrol terminal, a voltage divider having a plurality of taps, a sourceof voltage connected across said voltage divider, circuit meansinterconnecting said generator control terminal and said voltage dividertaps, said circuit means including a plurality of switches, each of saidswitches having a first terminal and a second terminal, each of saidfirst terminals being connected to a respective tap of said voltagedivider, a plurality of serially connected resistors, all said secondterminals being sequentially connected to junction points between saidplurality of resistors so that a single resistor interconnects saidsecond terminals of every adjacent pair of switches, and a connectionfrom the first resistor in the series to said generator controlterminal.

14. In a musical instrument, a duet device for accenting the highestnote and the lowest note of any plurality of notes simultaneously playedincluding a pair of voltage sensitive variable frequency electronicgenerators, a first control terminal connected to one of saidgenerators, a second control terminal connected to the other of saidgenerators, a voltage divider having a plurality of adjustable taps, asource of voltage connected across said voltage divider, circuit meansinterconnecting said generator control terminals and said voltagedivider taps, said circuit means including a plurality of switches, eachof said switches having a first terminal and a second terminal, each ofsaid first terminals being connected to a respective tap of said voltagedivider, a plurality of serially connected resistors, all said secondterminals being sequentially connected to the junction points betweensaid plurality of resistors so that a single resistor interconnects saidsecond terminals of every adjacent pair of switches, a connection fromthe first resistor in the series to said first generator controlterminal, and a connection from the last resistor in the series to saidsecond generator control terminal.

15. In a polyphonic musical instrument a solo device for accenting thehighest note of any plurality of simultaneously played notes including avoltage sensitive variable frequency electronic generator having acontrol terminal and an output terminal, a plurality of selected voltage points for controlling the frequency of said generator in accordancewith the notes played, selective circuit means interconnecting saidvoltage points and said control terminal, said circuit means including afriction switch and a memory circuit, said memory circuit including atime delay means to control the rate of change of voltage to saidcontrol terminal, said friction switch including means responsive to thetermination of the playing of any note being played alone or as one of aplurality of simultaneously played notes for disconnecting said controlterminal from all of said voltage points and thereby preventing a changeof voltage at said control terminal, said memory circuit being operativeto maintain said voltage at said control terminal substantiallyunchanged until another note or plurality of notes is played, and anoutput system cou pled to said output terminal.

16. A musical device as defined in claim 15 in which said time delaymeans includes a unilaterally conductive device for rendering the timedelay means effective when control voltage of one sense is transmittedto said source, and ineifective when control voltage of opposite senseis transmitted to said source.

17. In a polyphonic musical instrument a solo device for accenting thelowest note of any plurality of notes simultaneously played including avoltage sensitive variable frequency electronic generator having acontrol terminal, a voltage divider having a plurality of taps, a sourceof voltage connected across a voltage divider, circuit meansinterconnecting said generator control terminal and said voltage dividertaps, said circuit means including a plurality of switches, each of saidswitches having a first terminal and a second terminal, each of saidfirst terminals being connected to a respective tap of said voltagedivider, a plurality of serially connected resistors, all said secondterminals being sequentially connected to junction points between saidplurality of said resistors so that a single resistor interconnects saidterminal of every adjacent pair of switches, and a connection from thelast resistor in the series to said generator control terminal.

18. In a polyphonic musical instrument having a plurality of playingkeys operated to produce electrical signals to be applied to means forproducing solo tones, a friction switch having normally open contactscoupling said electrical signals to said solo means, an elongated membermounted in engageable relationship with at least some of said keys andfrictionally coupled to one of said contacts to close the contacts ofsaid friction switch upon the operation of any number of said keys andto open the contacts of said friction switch upon the release of any oneof said keys.

19. The combination set forth in claim 18 in which said elongated memberis a flexible cord with one end fixed and the other end frictionallycoupled to one of the contacts of said friction switch, and ismaintained in said engageable relationship by means of a pair ofintermeshed pulleys mounted upon each key.

20. The combination in claim 18 in which said friction switch comprisesa slide rod coupled to said elongated member, a pair of fixed contacts,a flexible electrical contact mounted between the pair of fixedcontacts, a friction member mounted in engageable relationship with saidslide rod and adapted to move said flexible contact relative to saidpair of fixed contacts from one of said fixed contacts to the otherfixed contact upon movement of said slide rod.

21. In an electronic musical instrument for simulating the effect of thesinging human voice, variable frequency tone generating means and afrequency control circuit coupled thereto, a keyboard, said keyboardcoupled to said control circuit to change the frequency of said tonegenerating means in accordance with the notes of a musical scale, and anoutput system coupled to said tone generating means, said output systemincluding an audio filter for establishing two peaks in the frequencyresponse curve of said output system, said peaks occurring atapproximately 900 cycles and 2300 cycles, said tone generating meansfurther including means for producing complex wave signals in which thesecond harmonic is of greater amplitude than the first harmonic.

22. In a polyphonic electronic musical instrument for producing solopercussive effects, an output system, a voltage sensitive variablefrequency tone generator having a frequency control terminal and anoutput terminal, a plurality of selected voltage points corresponding tothe notes of a musical scale, circuit means interconnecting said voltagepoints and said frequency control terminal, said circuit means includinga plurality of switches and a memory device, selective mechanical meansfor actuating said switches, said memory device including a frictionswitch, a capacitor having first and second access terminals, said firstaccess terminal being connected to one of said voltage points, saidsecond access terminal being connected through said friction switch tosaid switches to charge said capacitor to a voltage selected by theoperation of a corresponding one of said plurality of switches, and saidfriction switch being mechanically coupled to said mechanical means tobe closed upon actuation of any one of said plurality of switches and tobe opened upon deactuation of any of said plurality of switches, anormally inoperative gate circuit interconnecting said output terminaland said output system, percussive control circuit means for renderingsaid gate circuit operative, said percussive control circuit including asource of control voltage, a percussion switch, a storage capacitornormally connected to said source of control voltage by means of saidpercussion switch, a normally discharged timing capacitor coupled tosaid gate circuit, and means for operating said percussion switch totransfer the charge on said storage capacitor to said normallydischarged timing capacitor to render said gate circuit operative totransmit a percussive signal to said output system.

23. In an electronic musical instrument, a plurality of playing keys, avoltage divider connected across a source of regulated voltage, saiddivider having a plurality of preselected voltage points correspondingto notes in a musical scale; a plurality of switches sequentiallyconnected to said voltage points and adapted to be selectively operatedby said keys; a voltage sensitive utilization circuit having an inputterminal; a memory circuit coupled to said utilization circuit tocontrol'the voltage transmitted thereto, said memory circuit includingan electron conductive device having a control terminal, a capacitorconnected to apply a bias voltage to said control terminal, and circuitmeans between said plurality of switches and the capacitor for applyinga voltage thereto and including means for terminating the application ofsuch voltage when the operation of any playing key is terminated.

24. The device as defined in claim 23 in which said circuit meanscomprises a friction switch.

25. The device as defined in claim 24 in which said circuit meansfurther comprises a diode and resistor in parallel, serially connectedbetween said friction switch and said control terminal.

26. In a polyphonic electric musical instrument, a plurality of playingkeys; a plurality of balanced oscillators, the number of oscillatorsbeing half the number of playing keys, each of said oscillatorsincluding two electronic amplifying devices, a first output terminal,and a second output terminal, the signal frequency appearing at thesecond output terminal of each oscillator being twice the frequency ofthe signal appearing at the first output terminal of the oscillator; anoutput amplifier; and circuit means interconnecting the first and secondoutput terminals of said oscillators and said amplifier, said circuitmeans including key switches operable by said playing keys.

27. A multifrequency tone generator comprising: a multivibrator forgenerating variable frequency tone signals including first and secondtriodes each having cathode, plate and control grid elements, a pair ofbalanced capacitors connecting the plate element of each triode to thegrid element of the other triode, a pair of balanced grid resistors eachforming a timing circuit with a respective one of the pair of balancedcapacitors, a pair of bal- .anced cathode resistors connected in seriesbetween the cathode elements of the first and second triodes, a commoncathode resistor connecting the junction between the pair of balancedcathode resistors to a reference potential, and a source of operatingpotential coupled to the plate element of said first and second triodes;a frequency control circuit for providing a variable bias potential tothe grid resistors to control the frequency of the multivibratorincluding a voltage memory circuit; a circuit arrangement for furnishingD.C. voltages to the voltage memory circuit comprising a DC. potentialsource, a plurality of variable resistors coupled in series across theDC. potential source, a voltage divider circuit having a plurality ofelectrical input connections distributed at approximately equalresistance intervals there along, a tone selector means for selectivelycoupling junctions between the series coupled variable resistors tocorresponding ones of the input connections of the voltage divider, andswitching means operative in response to the coupling of an inputconnection to the corresponding junction for providing an output fromthe voltage divider to the voltage memory circuit and operative inresponse to the release of any coupling between the input connection andthe corresponding junction for uncoupling the output of the voltagedivider from the voltage memory circuit; a normally closed gatingcircuit coupled to receive the tone signals from said multivibratorcircuit; means responsive to the coupling of any one of said inputconnections of the voltage divider to its corresponding junction forproviding a control signal to said gating circuit, said gating circuitbeing responsive to said control signal for passing the tone signalsfrom the multivibrator; and an output arrangement for receiving the tonesignals passed by the gating circuit comprising a filter means forselectively attenuating lower frequency tone signals, a resistor outputchannel, and a combination filter means having first and secondfrequency peaks in predetermined frequency ranges corresponding to adesired tone quality, and means for selectively connecting the tonesignals passed by the gating circuit to one of said filter means or tosaid resistor output channel.

28. A multitone generating circuit comprising: a voltage controlledaudio oscillator circuit having an output frequency responsive to theamplitude of an applied control voltage; a circuit for generating avariable control voltage including a DC. amplifier having an outputterminal coupled to provide a control voltage to said voltage variableoscillator, 21 fixed potential source, a first voltage divider connectedacross said fixed potential source and having a plurality ofsubstantially evenly spaced connection points, a second voltage dividerhaving a corresponding plurality of substantially evenly spacedconnection points, a tone selection means for selectivelyinterconnecting corresponding connection points of the first and secondvoltage dividers, and switch means responsive to the operation of saidtone selection means for selectively coupling the output of the secondvoltage divider to the input terminal of the DC. amplifier; a storagecapacitor coupled to said input terminal of the D0. amplifier forproducing a voltage at the input terminal corresponding to the outputvoltage from the second voltage divider whenever said switch meansconnects the output from the second voltage divider to the inputterminal of the DC. amplifier and for maintaining a voltage at the inputterminal when said switching means disconnects the output from saidsecond voltage divider from the input terminal.

29. In a multitone generating circuit having a voltage controlledoscillator circuit for generating tones having a frequency proportionalto an applied control voltage, a circuit for generating a tone controlvoltage comprising: a fixed potential source; a first voltage dividercircuit connected across said fixed potential source and having aplurality of connection points distributed in accordance with tones in amusical scale; a second voltage divider circuit having a correspondingplurality of connection points substantially equally distributed andhaving an output terminal at one end; a voltage storage capacitorcoupled to provide the frequency control voltage to the voltagecontrolled oscillator; switch means operated in response to the couplingof any connection point of the first voltage divider with acorresponding connection point of the second voltage divider to conplethe output terminal of the second voltage divider to the storagecapacitor to develop the control voltage for providing the selectedtone, said switch means also being responsive to the disconnection ofany corresponding points of the first and second voltage dividers foruncoupling the output terminal of said second voltage divider from saidstorage capacitor to maintain the previously established controlvoltage.

30. The control voltage generating circuit of claim 29 in which saidswitch means comprises a flexible cord connected to a first stationarypoint, a rodconnected to the flexible cord, a spring connected between asecond stationary point and the rod, a plurality of mechanical means formoving the flexible cord perpendicular to its length in response to thecoupling of any corresponding connection points of the first and secondvoltage dividers, a first switch contact fixedly mounted adjacent therod, a second switch contact of a flexible material mounted to engagethe first switch contact, and a block arranged in sliding frictionalengagement with the rod mounting the second switch contact for movementwith the block.

31. A friction switch for completing an electrical circuit whenever oneof a plurality of rnechanical selection means is operated and for opencircuiting the electrical circuit whenever one of the plurality ofmechanical selection means is released comprising: an elongated flexiblemember coupled between two stationary points, said flexible memberincluding expandable spring means at one end coupled to one of saidstationary points, said flexible member being disposed for engagement byeach of said mechanical selection means to move the flexible memberperpendicular to its length in response to the movement of individualones of the mechanical selection means, a first switch contact, movablemeans for mounting said first switch contact in sliding frictionalengagement with a portion of said flexible member adjacent the springmeans, and a second switch contact fixedly mounted relative to said pairof stationary points and disposed to be contacted by said first switchcontact when said flexible member is moved longitudinally by actuationof the mechanical selection means, whereby the second switch contactcontacts the first switch contact to restrain further longitudinalmovement of the movable means.

32. The friction switch of claim 31 further comprising a stop memberfixedly mounted adjacent said second switch contact on the opposite sideof said first switch contact to be engaged by said first switch contactwhen the flexible member is moved longitudinally in the other directionby the release of any of said mechanical selection means for preventingfurther longitudinal movement of the movable means in the otherdirection.

33. In a polyphonic musical instrument having a plurality of playingkeys for producing solo tones from a voltage controlled tone generator,means providing a variable control voltage from a source, and circuitmeans for coupling the control voltage to control the frequency of saidtone generator, said circuit means including switch means coupled to beoperated by at least some of said playing keys to provide said controlvoltage to said tone generator upon the playing of at least one of saidsome of said playing keys and for disconnecting said control voltagemeans from said tone generator upon ceasing to play any one of aplurality of said some of said playing keys being simultaneously played.

34. An electronic polyphonic musical instrument for producing solo tonescomprising: a plurality of playing keys for selecting certain musicaltones; a voltage variable oscillator for producing oscillatory signalsat the frequency of these selected tones; voltage divider means dividinga control voltage for said voltage variable oscillator to produce saidselected tones; first switching means operated by said playing keys toselect the proper control voltage from said voltage divider means;second switch means serially connected with said first switch means forproviding the selected control voltage to said voltage controlledoscillator, said second switch means including switch control meansoperated by said playing keys for closing said second switch means uponoperation of any one or more of said playing keys and for opening saidsecond switch means upon release of any one of a plurality of saidplaying keys formerly operated simultaneously.

35. In a polyphonic musical instrument having a keyboard upon whichchords may be played, the combination comprising: a voltage controlledvariable frequency oscillator for generating the highest note of anychord played; a memory circuit for providing a control voltage to saidvariable frequency oscillator; a source providing a plurality of voltageamplitudes corresponding to the notes provided by keys of the keyboard;first switching means controlled by individual ones of said keys forcontacting selected ones of said plurality of discrete voltageamplitudes; second switching means serially connected with said firstswitching means for providing a selected discrete voltage amplituderepresentative of the highest note of the chord played from said firstswitching means to said memory circuit upon operation of any key on saidkeyboard and for uncoupling said first switching means from said memorycircuit upon releasing any of said keys played prior to releasing all ofsaid notes in a chord to disconnect said first switching means from saidsource.

36. In an electronic musical instrument, a device for simulating theeffect of the singing human voice comprising: the combination of avoltage responsive variablefrequency balanced oscillator, 21 memorycircuit comprising a vacuum tube having anode, cathode and control gridelements, said cathode element being connected to control the frequencyof said oscillator, a plurality of switching means, a voltage dividerhaving a plurality of selectable voltage points, a timing capacitorinterconnecting the grid and cathode of said tube, a charging resistorinterconnecting the grid of said tube and said switching means forlimiting the flow of charging current to said timing capacitor, and auni-directional circuit path having a relatively small resistancecompared to said charging resistor shunting said charging resistor forconducting a flow of discharging current from said timing capacitor,said switching means being adapted to connect said resister to diiTerentselected voltage points of said voltage divider to change the voltage onsaid timing capacitor, whereby the frequency of said oscillator isvaried gradually in one direction by the flow of charging currentthrough said charging resistor and is varied in discrete intervals inthe other direction by the flow of discharging current through saiduni-directional device in response to selection of diiferent switchingmeans.

37. In an electronic solo musical instrument having playing keys forselectively sounding various notes in a musical scale, the combinationcomprising: a variable frequency oscillator having a control terminal; amemory circuit connected to the control terminal for selectivelycontrolling the frequency of said oscillator; a control voltage sourcefor providing a selectable control signal to the memory circuit and tothe control terminal for controlling the frequency of said oscillator;switch means interconnecting said memory circuit to said source; andmeans responsive to the operation of at least one of said playing keysfor closing said switch means to connect said source to said memorycircuit and responsive to terminating the operation of any one of aplurality of simultaneously operated playing keys for opening saidswitch means to disconnect said source from said memory circuit tomaintain the voltage signal applied to said control terminal by saidmemory circuit constant until a subsequent operation of at least one ofsaid playing keys.

38. In a polyphonic electronic musical instrument, the combinationcomprising: a plurality of playing keys; a plurality of variablefrequency balanced oscillators at least some of said oscillatorsincluding a multivibrator circuit having two electronic amplifyingdevices, a selectively variable source of supply voltage responsive tothe operation of said keys for selectively varying the oscillationfrequency, circuit means interconnecting said devices with said sourceof supply voltage for causing said devices to conduct in alternatingfashion at selected audio oscillation frequencies corresponding todifferent notes in a musical scale, a first biasing resistor connectedbetween one of said devices and a common terminal, a second biasingresistor connected between the other of said devices and the commonterminal, said first and said second biasing resistors being connectedin series combination between said devices, a third biasing resistorconnecting said common terminal to said source, a first signal outputterminal connected to the series combination of said first and secondbiasing resistors at a balance point on one of said resistors where afirst signal voltage is developed at a frequency of twice the selectedoscillation frequency, and a second output terminal connected to one ofsaid devices where a second signal voltage is developed at the selectedoscillation frequency, the number of oscillators being less than thenumber of playing keys; utilization means including an audio amplifierand speaker means for sounding the different musical notes having thefrequency of the signal voltage applied thereto; and switch means forselectively connecting said first and second signal output terminals tosaid utilization means and operable in conjunction with said playingkeys.

39. In a polyphonic electronic musical instrument, the combinationcomprising: a plurality of playing keys; a plurality of variablefrequency oscillators having two electronic amplifying devices, a sourceof supply voltage selectively variable by operation of said keys forcontrolling the frequency of said oscillator, a separate biasingresistor for each of said devices, a first output terminal, each of saidseparate biasing resistors interconnecting one of the devices to saidoutput terminal, a third biasing resistor interconnecting said outputterminal to said source, at least one of said first and second biasingresistors being adjustable for balancing said oscillator so that a firstoutput signal appearing at said first output terminal across said thirdresistor contains principally even harmonics of the oscillatorfrequency, the amplitude of the second harmonic being at least fortydecibels greater than the amplitude of the first harmonic, and a secondoutput terminal connecting to one of said devices for providing a secondoutput signal at said oscillator frequency, the number of oscillatorsbeing less than the number of playing keys; utilization means includingan audio amplifier means for sounding notes at the frequency of theoutput signal applied thereto; and switch means for selectively applyingsaid first or second output signal to said utilization means andoperable in conjunction with said playing keys.

References Cited by the Examiner UNITED STATES PATENTS 2,274,199 2/1942Hammond 84-1.01 2,355,287 8/1944 Firestone 84-124 2,499,576 3/1950 Farr331-167 2,540,478 2/1951 Frost 331-144 2,544,017 3/1951 Golicke 331-1792,563,477 8/1951 Martin 84-125 2,720,133 10/1955 Morgan 841.24 2,918,57612/1959 Munch 84-126 3,048,719 7/1962 Grigsby 307-885 3,049,959 8/1962Meyer 84-1.17

DAVID J. GALVIN, Primary Examiner.

1. AN ELECTRONIC MUSICAL INSTRUMENT COMPRISING A VARIABLE FREQUENCY TONEGENERATOR HAVING A CONTROL TERMINAL, A KEYBOARD, AND MEANS FOR APPLYINGSIGNALS TO THE CONTROL TERMINAL TO CHANGE THE FREQUENCY OF OPERATION OFTHE GENERATOR IN RESPONSE TO THE MANIPULATION OF THE KEYBOARD, SAIDSIGNAL APPLYING MEANS INCLUDING UNILATERALLY CONDUCTIVE MEANS FORDECREASING THE FREQUENCY IN DISCRETE INTERVALS AND MEANS FOR IMPARTING APORTAMENTO EFFECT TO INCREASES IN THE FREQUENCY OF OPERATION OF THEGENERATOR.